The present invention relates to devices intended for transmitting and/or modulating in-phase and quadrature (or IQ) optical signals generated by an optical source.
IQ (In-phase and Quadrature) optical multilevel vector modulation formats such as Quadrature Phase-Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM) are notably used in telecommunication equipment and should be generalized in the coming years. As known by those skilled in the art the transmitters of the art implementing a QPSK/QAM function employ almost exclusively LiNbO3 Mach-Zehnder phase modulator arrangements (or nested Mach-Zehnders) with an external laser source, and sometimes GaAs or InP material based phase modulators.
These known technologies lead to large size and large energy consuming devices, and their speed operation appears to be limited by the driving power which notably increases when it becomes greater than 25/32 GBaud.
These drawbacks can be overcome by a new emerging technology based on prefixed optical phase switching with Electro-Absorption Modulators (or EAMs) made, for instance, of material of the InP family and integrated in interferometric waveguide arrangements. A footprint divided by 50 and an energy consumption divided by at least 4 are expected with this emerging technology.
However, with such an emerging technology, the optical phase state is extremely sensitive to the temperature due to thermally induced material index changes. Moreover, a wavelength channel change produces a phase state change because the optical index (i.e. the optical path (length times index)) is also wavelength dependent. For instance, a 10 nm optical path change may induce a prohibitive phase error that reduces the transmission performance. Therefore, complex monitoring and feedback optical/electronic circuits must be used for actuating the phase shifters, which increases the cost and then may render this technology unadapted to technical domains very sensitive to costs.